Forensic Science Intern&ion4 39 (18881257-282 Elsevier Scientific Publishers Ireland Ltd.

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STUDIES ON ASPHYXIA: ON THE CHANGES OF THE ALVEOLAR WALLS OF RATS IN THE HYPOXIC STATE. II. THE HYPOXIC STATE PRODUCED BY CARBON DIOXIDE AND METHANE GASES*

MASAHIKO MORITA and NORIKO TABATA

Department of Legal Medicine, Sapporo Medical College, Nishi 17, Minumi 1, Chuo-ku, Sapporo 060 IJapad

(Received January 19th. 19881 (Revision rleceived February 19th, 19881 (Accepted April 14th. 19881

Summaqy

Experimental studies were presented here concerning death by asphyxia due to the inhala- tion of carbon dioxide and methane gases. The morphological changes were almost the same as those demonstrated in our previous report. The authors concluded that the morphological changes in the lung tissue were not attributable to the chemical specificity of gases used in the experiment but to the decrease of oxygen.

Key worda Asphyxia: Hypoxia; Carbon dioxide; Methane; Surfactant

Introduction

We previously published a paper [l] on the morphological changes in rat’s lung in bypoxic state in which lattice-like and/or tubular myelin appeared in the alveolar space with or without homogeneous substance. With the higher magnification by the electron microscopy, the homogeneous substance revealed a debris-like structure and seemed to be closely connected with the lattice-like structures and/or the tubular myelin mentioned above.

In thi;s paper we present the morphological findings by electron micros- copy of rat’s lung which has inhaled air containing carbon dioxide and meth- ane gases.

Each gas was drawn into the observation box in various concentrations with nitrogen gas and a constant 20% oxygen.

Materials and Methods

The Wistar albino male rats used in this experiment were put into the observation box to inhale air containing 20% oxygen and each gas in a

*Part I published as: Forensic Sci. Int.. 2’7 (1985) 81-91.

0379-0738/88/$03.50 0 1988 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland

controlled proportion with nitrogen. All gases were controlled with a fluorometer.

Carbon dioxide iC0,) (1) Gas content of the inhaled air was maintained at 20% oxygen, 3Om50%

CO, and 50~20% nitrogen gas (NO,) for the first 30 min. At 30 min from the start of the experiment, both oxygen and nitrogen were withdrawn and entirely interchanged with CO,. (2) The effects of 100% CO, in the observation box was also examined.

Methane KXl,I (1) Eight percent methane and 20% oxygen were drawn into the observa-

tion box for about 1 h and then the oxygen was withdrawn. (2) Methane gas was drawn into the box with gradual increase to a final flow volume of 2.5 I/ min. (3) Tissue preparation for morphology. Lung tissues were taken from all

Fig. 1. Surface of the alveoli is markedly wavy and the lumen is filled with debris-like structures (D) in which tubular myelin (+I is ascertainable surrounding a round space (API through which air has apparently passed. GAC = Great alveolar cell. Carbon dioxide case. 7300 x .

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rats immediately after death and were put into the fixatives in the ordinary way for both light and electron microscopic examinations. The staining meth- ods for morphology were the same as those in the previous examinations [2].

(1) F&&s inhaling carbon dioxide died from 10 to 30 min after the with- drawal of oxygen. Their lungs were dark red in colour and markedly shrunk; these macroscopic findings and both the light and electron microscopic find- ings were the same as in the rats killed at 30 min after the beginning of inhalation.

Light microscopic observation Homogeneous substance which was pale pink in ithe H-E stained section was observed in the majority of alveoli. No staining revealed any particular positivity of the substance except the pale pink by H-E.

Fig. 2. Similar findings as shown in Fig. 1.8700 x .

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Electron microscopic observation. Morphological features were basically the same as those of rat’s lung in the 5% oxygen group. The surface of the alveoli showed an irregular wavy appearance, reflecting the shrinkage of the lung due to the decreased air in the alveoli. The substance which was seen as homogeneously pale pink with the light microscope was a massive accu- mulation of the debris-likle figures in which tubular myelin and membraneous structures were scattered abundantly (Fig. 1). The densities of the debris varied (Fig. 2).

The appearance of fibrin fibers in the debris-like substance and erythro- cytes observed occasionally along with fragments of thrombocyte in the alveolar cavities was the outstanding finding in this group of experiments (Fig. 3).

(2) Rats inhaling methane gas in the observation box moved like those in 5O/b oxygen group [l].

Fig. 3. Wavy appearance of the alveolar surface can also be seen. The appearance of fibrin con- figuration (F) intermingled with myelin figures is the most outstanding finding. The squamous alveolar cell (type I celk SAC) seems intact. Carbon dioxide case. 10,000 x .

261

Light microscopic observation. The accumulation of the homogeneous sub stance in the alveoli which was stained pale pink was the same as in the case of CO, gas and the previous examination [l].

Electrlon microscopic observation. Irregularity of the surface of the alveoli was the same as observed in the lung’s tissue of the CO, group. Lattice-like structures and/or tubular myelin were observed rarely only in small amounts and randomly in the alveoli. There were no remarkable changes attributable to the inhalation of methane gas in the great pneumocytes.

Discussion

We do not encounter death through the inhalation of CO, gas so often, but death is seen in a limited number of places such as silos storing hay for livestock, old and unused mines and some such narrow spaces in which air is easily displaced by naturally produced gas.

On the other hand, death by the inhalation of methane is rather more fre- quent, es#pecially in coal mine explosions and explosively discharged gas and, more rarely, in old and unused wells or tanks at *sewerage works. These two gases were therefore, chosen for the experiment in examining the relatively hypoxic state.

There may be some conditions under which air is displaced by gases pro- duced naturally or explosively discharged, for instance, from a cylinder by mishandling of a valve with a consequent decrease in oxygen. The morphol- ogical findings of this experiment in the surfactant in the alveolar space were the same as those which we observed in the previous experiment using 5% oxygen and those which have been reported in many experiments [2- 111. Twenty percent oxygen was maintained for the first 30 min of the exper- iment to discover the specific effect of CO, and methane on the morphologi- cal changes in rat lung compared with that of rats in 5% oxygen and to examine the distribution of carbon dioxide in several organs. No change in the alveolar wall attributable specifically to CO, was found however except such change as was similar to those observed in the 5% oxygen group [l].

With the findings above observed, we concluded that the morphological changes in a lung tissue after the inhalation of either gas could not be attrib- uted to the gases per se but to decreased oxygen.

Acknowledgements

The authors wish to express their cordial thanks to Miss M. Suzuki for her technical assistance in preparing ultra-thin sections for the electron microscopy and to Mr. S. Ohtani for preparing sections for the light microscopy. The authors are also grateful to Professor M. Mori of the Department of Pathology, Section 2, Sapporo Medical College for his valua- ble advice and suggestions. A part of this work was supported by the Grant- in-Aid (615702941 for Scientific Research from the Ministry of Education, Science and Culture, Japan.

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